1. Field of the Invention
This invention relates to apparatus and method for magnetic measurement, and in particular to measurment of the magnetic remanence-thickness product of a thin magnetic layer.
2. Description Relative to the Prior Art
The measurement of the magnetic remanence of a magnetically recorded layer is an important parameter in determining the recording effectiveness of the magnetic layer. In the prior art, measurement of the magnetic remanence of a recorded medium has conventionally been accomplished by use of a B-H loop tester which allows the determination of the remanent magnetization M.sub.r. This method is described in U.S. Pat. No. 4,901,016 issued to Kusutani et al entitled "Device Having a Magnetic Head for Measuring Magnetization Characteristics of a Magnetic Thin Film" (Column 1 and Column 2, lines 1-47). As applied to determining the magnetic remanence of a thin film magnetic strip, they point out the necessity of using a sample consisting of about 10 layers of the magnetic film to provide sufficient magnetic material for the measurement, and that this method of measuring the remanence of a thin film strip is extremely cumbersome.
For thin recorded layers, the product of the magnetic remanence, M.sub.r, times the layer thickness,.delta., is generally considered a more useful parameter in evaluating the recording effectiveness of a magnetic layer than the remanence alone. The M.sub.r .delta. product measures the magnetic flux carrying capacity per unit width for a magnetized layer, and where, as is generally practiced in recording data, the recorded information is laid down in the form of tracks the M.sub.r .delta. product is directly related to the flux strength/unit track width, and hence to the effectiveness of the medium for recording.
Generally the M.sub.r .delta. product is small and difficult to measure accurately. For example, in a hard disk drive, the thickness of the magnetic film may be 750 angstroms and the remanent magnetization may be on the order of 500 emu/cm.sup.3, resulting in the small value of the M.sub.r .delta. product of 4.times.10.sup.-3 emu/cm.sup.2. In the present invention, apparatus is disclosed for measuring the M.sub.r .delta. product of such magnetized thin film material in an accurate and repeatable manner.